Coronary artery bypass surgery has found wider indications and is now also believed to be indicated in certain patients with signs of acute ischemic heart disease. The hereto needed diagnostic workup requires the performance of selective coronary angiography and cardiac angiograms which under those circumstances are likely to involve greater risks to the patient. The purpose of the proposed experimental study is to define more accurately the side effects of angiographic contrast agents on myocardial function under both basal and graded ischemic conditions. An animal model, in which a part of the coronary circulation is separately perfused with oxygenated blood, will be used to examine the time course of changes in the mechanical characteristics of the relevant myocardial heart area to graded reduction of flow and to be compared with the normally perfused myocardium. Volume and flow controlled injections of different radiographic contrast agents of equal concentration of iodine will be performed at different degrees of blood flow reduction and their effect on myocardial tension development will be recorded, which will be with simultaneous angiography subjected to densitometric studies. Similarly, the events during the period of recovery following restoration of normal blood flow levels will be studied. Additional, simultaneous extractions of arterial and coronary venous blood will be analyzed for levels of serum electrolytes (Na, K, Ca), in order to explore the possible relationships between different contrast preparations and electrolyte leakage induced by the chelating agent; and cine angiogram subjected to densitometry to correlate flow and intensity of myocardial blush. It is expected that the results will provide more accurate information as to the effects of contrast on the normal and ischemic myocardium. The results should also be useful as guidelines to the design of optimal contrast medium preparations and their use in selective coronary arteriography in patients with advanced ischemic heart disease.